It is generally known to protect products that are sensitive to moisture and oxygen from harmful atmospheric influences by packaging them in plastics materials. Moisture-sensitive products may, for example, be surrounded by a plastics material film which is practically impermeable to water molecules. A film made of a high density polyethylene (HDPE) or made of a polyvinylidene chloride-methylacrylate copolymer (PVDC-MA) can be used as a barrier against the penetration of moisture, for example. Films made of oriented polypropylene (oPP), optionally metallised, or metallised polyester films, are also used as a barrier material against the penetration of moisture. Furthermore, metal films are known as a barrier material against the penetration of moisture and/or oxygen and are often used in a composite with plastics material films. A good barrier effect against water vapour and gases can also be achieved with a layer of ethylene-vinyl alcohol copolymer (EVOH).
Although laminates with barrier layers with a high penetration barrier effect against moisture and oxygen are known nowadays, the penetration of moisture cannot be completely prevented, specifically in sealed packagings, as the edges of the laminates are not protected by the barrier layer. Moisture and oxygen can penetrate by way of these unprotected edges in the region of seals into the interior of hot-sealed packagings and impair the quality of moisture-sensitive products.
Multi-layer films with a barrier layer and with a sealing layer containing moisture-adsorbing material are known from WO-A-2004/080808. The films are used for packaging moisture-sensitive articles, such as, for example, diagnostic test strips, and are either, after folding, sealed against themselves or against a second film. Calcium oxide (CaO) is preferably used as the moisture-adsorbing material with a strong water-binding action.
It is known from WO-A-2007/104344 to use blister packs with a blister base part made of a laminate with a barrier layer against water vapour and gases to package moisture-sensitive products, such as tablets and powders. In addition, a layer made of polyolefin and containing, for example, CaO as the drying agent is arranged on the side of the barrier layer, which is directed against the inside of the blister base part and against a cover foil closing the blister base part. A cover film designed as a push-through foil, for example, has the following layer structure: sealing layer/aluminium foil/print undercoat lacquer/printing/print top coat lacquer.
Typically, a push-through foil of blister packs has an aluminium foil with a thickness of 20 μm in the “hard” state. In order to ensure the push-through capacity even for weaker people, such as, for example, elderly people, the inner layer required inter alia for sealing against a blister base part may not exceed a certain thickness either. A conventional push-through foil with an LDPE coating as the sealing layer is, for example, constructed as follows:
Lacquer, 1 to 2 g/m2/aluminium foil hard, 20 μm/primer 1 g/m/LDPE 15 g/m2.
The water absorption capacity of blister base parts with an inner layer containing drying agent is limited because of the thickness of the inner layer which is limited to weights per unit area of the inner layer including the drying agent of typically about 35 to 65 g/m2. The drying agent fraction is typically about 30 to 50% of the total weight per unit area of the layer which is loaded with drying agent. In order to also dry “moist tablets” with the aid of a drying agent, however, as high as possible a water absorption capacity is basically to be aimed for in the blister pack.